Cardiorespiratory endurance -- also referred to as cardiovascular fitness, cardiorespiratory fitness or aerobic fitness -- is an essential component of both physical fitness and all-around good health. Specifically, cardiorespiratory endurance refers to the ability of the heart, lungs and circulatory system to deliver oxygen to working muscles for sustained periods of time. A cardiorespiratory endurance training program should include activities that elevate the heart rate and involve the body's large muscle groups.